The invention concerns an NMR-spectrometer with a magnet system that produces a magnetic field which is nearly homogeneous within a specified region, with a sample holder in said homogeneous field region and a sample changer comprising a sample magazine and devices to sequentially transfer one sample at a time from the magazine to the holder and back.
There are many known embodiments of NMR-spectrometers. Some of them include sample changers which allow continuous around-the-clock use, for example the Bruker AM-series NMR spectrometers. Although these sample changers permit automatic collection of spectra in rapid sequence, the time needed for taking one spectrum depends strongly on the spin-lattice relaxation time T1 since this relaxation time determines the time period during which a sample must be prepolarized before it can be excited to take a spectrum. The time necessary for prepolarization is typically 5.times.T1. Therefore measurements of samples with long relaxation times T1 require particularly long times especially when these relaxation times are several hours. In particular with solid samples T1 is very large whereas the spin-spin-relaxation time T2 is relatively small. Therefore it is not possible to prepolarize the sample in a second magnet with subsequent transfer to the spectrometer magnetic field, since during the transfer the sample would have had to have passed through a region of small and changing magnetic field strengths (the earth's field). As a result, the prepolarization of the sample would have been destroyed (see e.g. R. Dupree and M. E. Smith, JMR 75, 153 (1987 ) and C. A. Fyfe, Solid State NMR for Chemists, C.F.C. Press, Ontario, Canada 1983).
NMR-spectrometers with a sample changer and sample magazine are known e.g. from U.S. Pat. No. 4,581,583. U.S. Pat. No. 4,654,592 discloses an NMR-spectrometer wherein, within a homogeneous magnetic field region, a stator housing supports separated parallel rotors each containing one sample. Separate RF-coils can be used for each sample or both samples can be inside a common coil. The rotors are the sample holders. There is no provision for a magazine from which the samples can be transferred to and from the sample holder. If a single RF-coil is used the measurement of the different samples takes place necessarily simultaneously. Even when several RF-coils are used simultaneous measurement is also envisioned. U.S. Pat. No. 4,654,592 does not disclose the possibility of prepolarizing the sample in a magnetic field for a long time without performing a measurement and afterwards transferring this sample to the actual measuring region, where the RF-coil is located and the magnetic field is sufficiently homogeneous.
NMR-spectrometers with a sample changer and sample magazine are known e.g. from U.S. Pat. No. 4,581,583. U.S. Pat. No. 4,654,592 discloses an NMR-spectrometer wherein, within a homogeneous magnetic field region, a stator housing supports separated parallel rotors each containing one sample. Separate RF-coils can be used for each sample or both samples can be inside a common coil. The rotors are the sample holders. There is no provision for a magazine from which the samples can be transferred to and from the sample holder. If a single RF-coil is used the measurement of the different samples takes place necessarily simultaneously. Even when several RF-coils are used simultaneous measurement is also envisioned. U.S. Pat. No. 4,654,592 does not disclose the possibility of prepolarizing the sample in a magnetic field for a long time without performing a measurement and afterwards transferring this sample to the actual measuring region, where the RF-coil is located and the magnetic field is sufficiently homogeneous.